Over the years deposit formation in internal combustion engines has been a continuing problem. The amount of deposit formation had been controlled to some extent by the use of antioxidants and metal salts, particularly highly basic metal salts, of various organic acids. While these efforts provided some benefit, a particularly troublesome type of deposit referred to as "sludge" continued to form in internal combustion engines. This sludge accumulated on the various internal parts of the engine and caused sluggish operation, increased wear and sometimes resulted in blocked oil passages resulting in extensive wear and/or failure of the engine. The only way known to control accumulation of harmful amounts of sludge was to change the engine oil at frequent intervals, usually every 30 days or every 1,000 miles of operation.
By the late 1950's and early 1960's, additives were developed which were found to control sludge formation. These additives, generally referred to as "ashless dispersants", and refinements thereof, revolutionized lubricant additive chemistry and resulted in the ability to extend oil change intervals to up to as long as one year of more.
Recently, and particularly in Europe, a new type of engine deposit has been observed. This deposit is sometimes referred to as "black sludge" or "German sludge" because it was first observed in Germany. Black sludge causes operational problems similar to those observed with the earlier observed sludge formation. Conventional engine oil additives, including the ashless dispersants, have not effectively controlled formation and/or accumulation of black sludge. Accordingly, a method for controlling the formation and/or accumulation of black sludge in an internal combustion engine would be of considerable value.